In recent years, the way of saving energy is investigated in various fields in view of preventing global warming. Progress has been made in the information apparatus such as an image forming apparatus which can be operated with low energy by introduction of energy saving during stand-by time of the apparatus, and at the same time, it has been investigated the way of lowering fixing temperature in the fixing process which consumes most energy.
Generally speaking, when a toner is designed to have an ability of corresponding to low-temperature fixation, it will become inferior in blocking resistance or heat-resistant storage property. However, in order to make compatible both low-temperature fixability and blocking resistance, there is disclosed as a toner for electrophotographic image formation, in which an ABA type block copolymer consisting of styrene acrylic copolymer blocks is employed as a binder resin, for example refer to Patent document 1. It is supposed that when such toner is used in a fixing process, the affinity of a block copolymer and an image carrier will be increased during heat melting step of the toner on the image carrier, such as paper, and that compatibility of low-temperature fixability and blocking resistance will be improved.
However, since there was a limitation for the lowest glass transition temperature of a block copolymer from the viewpoint of heat-resistant storage property, it was still not enough to achieve sufficient improvement in low-temperature fixability was enough.
Moreover, in Patent document 2, there is disclosed a suspension polymerization toner containing a binder resin composed of a styrene-acrylic resin as a main resin to which is added a styrene-diene block co-polymer as a technique of making compatible of low-temperature fixability, heat-resistant storage property and blocking resistance. By using such toner, it is possible to apply the effect of encapsulating a wax in the styrene diene block copolymer during the particle producing process. And it is supposed that blocking resistance can be improved without raising fixing temperature.
However, since the styrene diene block copolymer is not distributed homogeneously in the main resin, there is problem that a hot offset phenomenon occurs. Moreover, there is another problem that fold fixability is low. Namely, the obtained fixed image becomes weak, and when this fixed image is folded, the fixed image at the folded portion will be broken and it will be peeled off.
On the other hand, it is proposed a core-shell structure toner as a technique to improve compatibility of low-temperature fixability and heat-resistant storage properties of the toner, and although low-temperature fixability is acquired to some extent after heat-resistant storage property is secured by using such toner, there is a problem that fold fixability is still low.
Moreover, there is disclosed a toner using the rubber-like substance obtained by cross-linking a binder resin with a crude rubber as a technique of achieving compatibility of low-temperature fixability and blocking resistance in Patent document 3. However, sufficient low-temperature fixability was not acquired in the toner having a small particle size.    Patent document 1: Japanese Patent Application Publication (it is called as JP-A) No. 3-217849    Patent document 2: JP-A No. 7-181740    Patent document 3: JP-A No. 8-305079